Domestic case studies from the shop

April 1, 2021
See how these five vehicles that were brought into the bay were diagnosed and repaired.

Our first domestic vehicle is a 2016 Dodge Grand Caravan 3.6L with 16,346 miles on it. It came in with a complaint of rough running and an illuminated MIL. After our initial analysis, we connected our scan tool and obtained the following DTC: P219A (Air-Fuel Ratio Cylinder Imbalance Bank 1) 

This was not the DTC we expected, since the engine was running so rough and seemed to exhibit a severe misfire. Looking up the DTC in ProDemand provided us the following information on what can cause the code. There were several different issues listed in the following order: 

  • Intake manifold leak 
  • Fuel injector
  • Variable cam lift failure
  • Camshaft/valvetrain problems
  • Ignition system
  • Engine mechanical issue on a specific cylinder. 

After my tech Bill completed his diagnosis, he continued by checking relative compression and vacuum using a pressure transducer to rule out common camshaft failure issue. The results of the test did not uncover any problems, so Bill thought it was time to move back to checking the ignition system once more. No other issues were found 

His next step was to take another look at scan data to view fuel injector pulse width on all cylindersWhat he found was injection pulse width on cylinder 1 at 2400 uS (microseconds), while all the other cylinders were at 1900-2000 uScame over to help Bill with this issue. We connected an amp clamp on injector number 1 circuit, and it displayed only 650 mA on the eScope (Figure 1)Next, we checked cylinder 3 injector current (Figure 2), which was the easiest to obtain a reading from. It displayed the expected 950 mA.  

I decided to take out our OTC Injector tester. It allows for an easy connection to fuel injectors so that a resistance and voltage coil test can be performed. The results of the resistance test on cylinder 1 injector were 32 ohms of resistance (the specification is only 12-15 ohms). Check out the video I made and put up on the TST seminar YouTube channel:  

Now this made sense. Since high resistance yields lower amperage, the injector could not pull the proper current to open the pintle for a long enough duration. To confirm that it was not a computer driver problem, we connected the wires from number 1 injector to number 3 injector and vice-versa. We found that the drivers were good. The test confirmed our resistance findings — that there was an internal resistance issue (the terminal ends were clean and both injector drivers were able to produce proper amperage on a good injector). We looked at the emission warranty and recommend to the vehicle owner that they contact the dealer to get the vehicle repaired for free. The dealer warranted the injector, and the Caravan was now running as designed again with one happy customer.  

2014 Jeep Patriot 2.4L “Wont idle/Low-Power” 

Our next vehicle problem was a 2014 Jeep Patriot 2.4L with 80,158 on the odometer. The complaint was that the engine would not idle, and the engine did not seem to produce its normal power. The vehicle owner also noticed a lightning bolt illuminated on the dashboard when the problem occurred. The Patriot owner was able to slowly drive the Jeep into us and provide a description of the problemWe started our analysis by the usual visual inspection before connecting our scan tool. The scan tool data uncovered the following DTCs (Figure 3):  

  • P0221- Throttle Position Sensor Circuit Performance 

  • P2135 Throttle Position Sensor Correlation 

  • P0325 Knock Sensor 1 Circuit 

We thought that the first place to start would be an inspection of the electronic throttle blade and the sensors. The blade looked a bit dirty but not to where it should have caused an issue. We cleaned the throttle and checked for binding, but no issues were found. The next step was to check the 5-volt reference for the two sensors, followed by making sure the voltage on the sensor wire did not drop out when moving the throttle from the stop position to wide open.  

When the P2135 fault is present, there is usually a difference between the calculated MAP sensor signal, compared to the TPS 1 input. According to service information, the same calculation is done on TPS 2 and if there is a large enough difference between the two sensors the PCM will store the P2135. Possible causes for the DTC are: 

  • High resistance in the 5-volt circuit 

  • High resistance in either one of the sensor circuits 

  • A throttle body issue 

  • The PCM is defective 

Before making any decision on replacing the throttle body, my tech Franklin moved on to diagnosing the other manufacturer-specific DTC. The P2135 Throttle Position Sensor Correlation issue would need to be carefully checked out before making a call on the throttle body. Reading up on the circuit uncovered that both sensors share the same 5-volt reference signal and common ground. The voltage for TP 1 starts at 0.5 volts and goes up to 4.3 volts. The second TP sensor starts at 4.5 volts and goes down to 0.7 volts.  

The knock sensor fault was diagnosed as a bad Knock sensor and replaced. With everything reading correctly, the DTCs were cleared, and the engine was restarted. Just about instantly, the MIL returned, indicating that there was a problem either with the throttle body adjustment, throttle body assembly, and /or PCM. Franklin followed all the correct steps before he decided to replace the throttle body assembly as described in the service information. With the new throttle body installed and initialized, the vehicle was started up. Neither the MIL nor lightning bolt illuminated. Franklin took the vehicle for a test drive and upon return, the MIL and lightning bolt was back on.  

Checking the complete circuit out again led to his decision to call for the replacement of the PCMA new Chrysler PCM was installed and programmed (using the Chrysler Wi-Tech scan tool and software)With the new throttle body and PCM, the Jeep was, once again, taken for a test drive. The results of the test drive were no MIL or lightning bolt illuminated. The Patriot ran great on multiple test drives and was returned to the owner.  

2000 Jeep Grandon Cherokee 4.7L “Start/Stall”  

The next problem was another Jeep — a 2000 Grand Cherokee 4.7L with 100,464 miles accumulated. It was towed in as a start and stall. After Bill, my lead tech, checked all the basics, he found that the scan tool could not communicate with the PCMHis approach to this problem was to perform a visual inspection where he found a bunch of leaves and pine needles near the cowl and underhood area. After cleaning them up, look at what we found — a broken wire in the harness (Figure 4).  

Bill’s next move was to pull up the wiring diagram in ALLDATA to view the connector and communication lines. He started testing each of the communication lines in the harness and found the following at Pin 2 — a straight line of the voltage of just over 8 volts (Figure 5). At Pin 4 no voltage was found (Figure 6). Measuring at Pin 5 displayed some communication that went up to 7.5 volts but not always going to ground (Figure 7). The rest of the pins had similar readings, even after the broken wire was repaired.  

Since the drains were clogged with debris, I suggested that Bill take a good look at the bulk connector male and female pinsWhat he found was a bulk connector that looked like it took a long swim underwater. Looking at the bulk connector, you can see why just repairing the broken wire did not fix the problem (Figure 8). The issue here caused voltage drop and needed to be cleaned with an electrical cleaner, then coated with Stabilant 22A (a contact enhancer).  

After the cleanup and coating of the wire harness connector male pins with Stabilant 22A, the Jeep was able to communicate as seen, with the voltage going from 0 to 7.5 volts (Figure 9)Bill reached in the Jeep then turned the ignition key, resulting in the 4.7L engine starting. The Jeep was now running well and returned to the owner with everything communicating as designed.  

2011 Dodge Journey 3.6L “No-Start” 

Here goes another one — a 2011 Dodge Journey 3.6L V6 with 88,206 miles on the clock. It had a crank, no-start issue. Upon an inspection of the problem, it sounded like the engine had compression issue. Before putting the cart before the horse, we checked the fuel system for proper pressure and flow and the ignition system for good enough spark, leaving a possible compression issue as a likely cause. 

As the engine was cranked it would start, but the engine sputtered and ran very rough. Along with the rough-running engine, there were plumes of black exhaust smoke along with highly elevated exhaust gas readings (Figure 10). We were just barely able to back the vehicle out of the bay and take it for a good test drive.  

During the test drive, the vehicle was stopped and restarted a few times then ran rough before clearing up. The Journey was driven back into the bay to perform a relative compression test. The results were not consistent and showed a compression difference on a few different tests before clearing up and obtaining a passing gradeWe took a time-out and thought about what could cause the engine to run rich then clear up. We concluded that since this engine utilized cam phasers, there may be an issue in that system since it occurred when the temperature was cold. To rule out a problem with the cam phasers we changed the oil and parked the vehicle outside in the cold weather to see if the problem would show up again. The fix for this problem Dodge was changing the oil and filter so the cam phasers could operate properly. 

2015 Jeep Grand Cherokee Hybrid “Severe Misfire”  

Moving on to another Chrysler product — a 2015 Jeep Grand Cherokee 3.6L / 24 with 87,671 miles had a severe misfire. The story behind this Jeep is that it was at another shop that was not sure what was causing the cylinder 6 misfireThe Jeep owner told us that the other shop had first diagnosed the problem as an ignition issue, which was followed by a fuel injector diagnosis before finally thinking that the issue may be a camshaft problem 

Now, you cannot always believe the vehicle owner, so we just explained that we would need to diagnose the vehicle and make a conclusion based on our testing. I understand it is easy for a vehicle owner to lose confidence in any shop that cannot provide them with an accurate diagnosis. When the owner no longer had confidence in that shop, they called RepairPal back for another shop recommendation. Our shop was the one recommended by RepairPal, so the owner decided to have their Jeep towed in for us to diagnose and repair.   

We started our diagnosis as usual with a good visual that Bill and I performed. This was followed by a vehicle scan and a cylinder pressure transducer test. Test results indicated a problem related to a valvetrain issue. We prepared an estimate and provided all the details, including pressure transducer waveforms, to the Jeep owner who now informed us that we had to speak to a warranty company. We were now looking at additional work added to this job since we had to call the warranty company to obtain approval.  

Dealing with warranty company is always a hassle, as in this case. We thought that we should perform a complete valve job on this 3.6L engine and not a half-ass job. The warranty company would not even allow us to send the head to the machine shop to find out the exact problem area of the head that was causing the problem. They already made up their mind and only approved the replacement of a signal cylinder head and one spark plug. Trying to get the warranty company to go for a new thermostat, flush and oil change and other needed parts just were not going to happen.  

Since they did not approve anything other than one cylinder head and gaskets, we spoke to the Grand Cherokee owner. We explained that an engine with 87k plus should have the following repairs performed: 

  • The other cylinder head checked out and reconditioned 

  • Thermostat replacement 

  • Flush oil and filter change 

  • New belts 

  • Spark plugs  

  • PCV valve 

  • Air filter 

The customer agreed with everything we suggested but did not want to do anything to the other cylinder head. This made us feel a bit uncomfortable repairing this Jeep. Once everything was approved, we started our removal, clean up, and install to get this engine running the best we could. We found that the camshaft was worn a bit, but that was not the main problem with the number 6 cylinder issue (Figure 11). The problem was a burnt valve that could have been repaired without a cylinder head replacement. However, since we were not allowed to send the heads to the machine shop and get the engine up and running the right way, we had to do it their way. So far, the Jeep is still running good, the customer is happy and came in with a few more of their vehicles for repair. 

I hope these domestic case studies were helpful to you and provide some guidance in diagnosing problem vehicles you may encounter. 

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